Transmission apparatus and transmission method using a plurality of divided frequency bands in a communication band

ABSTRACT

A radio communication apparatus capable of alleviating a burden in setting a transmission format and suppressing increases in the scale of the apparatus. In this apparatus, space multiplexing adaptability detection section detects space multiplexing transmission adaptability for divided bands obtained by dividing a communication band to which Ns subcarrier signals belong in multicarrier transmission and to which a plurality of subcarrier signals belong, and outputs the detection results. Transmission format setting section sets a transmission format when carrying out radio transmission based on the detection results from space multiplexing adaptability detection section.

BACKGROUND

Technical Field

The present invention relates to a radio communication apparatus andradio communication method used for a digital radio communication systemwhich employs a multicarrier scheme.

Description of the Related Art

In recent years, there are increasing demands for capacity and speedenhancement of radio communication, and researches on methods forimproving effective utilization of limited frequency resources have beenactively conducted. As one of the methods, a technique utilizing spatialareas is attracting attention. One such representative method is atechnique whereby spatial orthogonality in propagation paths is utilizedand different data sequences are transmitted using physical channels ofthe same code at the same time instant and at the same frequency.Examples of such a transmission technique include Space DivisionMultiple Access (SDMA) (e.g., see Non-Patent Document 1) wherebydifferent data sequences are transmitted to different mobile stations,and a Space Multiplexing (SM) (e.g., see Non-Patent Document 2) wherebydifferent data are transmitted to the same mobile station.

In the above described SM, an apparatus on the transmitting sidetransmits different data sequences from a plurality of antennas providedon the apparatus on the transmitting side at the same time instant, atthe same frequency and using physical channels of the same code for eachantenna, while an apparatus on the receiving side separates signalsreceived through a plurality of antennas provided on the apparatus onthe receiving side into different data sequences based on a channelmatrix indicating a propagation path characteristic between thetransmission/reception antennas (hereinafter referred to as “BLASTtype”) and thereby enables the efficiency of frequency utilization to beimproved. When SM transmission is carried out, it is possible to expandthe communication capacity in proportion to the number of antennas ifthe apparatus on the transmitting side and the apparatus on thereceiving side are provided with the same number of antennas in anenvironment in which there are many scatterers between the apparatuseson the transmitting and receiving sides under a sufficient S/N (signalpower to noise power ratio).

Furthermore, in realizing considerable increases in capacity and speedenhancement of radio communication, it is important to improve toleranceto multipath or fading. A multicarrier transmission scheme is oneapproach to realize this and in particular an orthogonal frequencydivision multiplexing (OFDM) transmission scheme is adopted forterrestrial digital broadcasting and wideband radio access systems.

One example of a transmission scheme in which SM transmission is appliedto this OFDM transmission is described in Non-Patent Document 3. Underthis transmission scheme, when there is no multipath that exceeds thelength of a guard interval, each subcarrier can be regarded as narrowband transmission, that is, flat fading transmission. For this reason,many examples have been reported where a channel matrix is calculatedfor each subcarrier and SM transmission is carried out based on thecalculated channel matrix H.

Non-patent Document 1: “A Study on a Channel Allocation scheme with anAdaptive Array in SDMA”, Ohgane, T., et al., IEEE 47th VTC, pp. 725-729,vol. 2, 1997

Non-patent Document 2: “Layered Space-Time Architecture for WirelessCommunication in a fading environment when using multi-elementantennas”, Foschini, G. J., Bell Labs Tech. J, pp. 41-59, Autumn 1996

Non-Patent Document 3: “On the Capacity of OFDM-based SpatialMultiplexing Systems”, IEEE Trans. Communications, vol. 50, pp. 225-234,2002

BRIEF SUMMARY Problems to be Solved by the Invention

However, the conventional radio communication system needs to calculatea channel matrix for each subcarrier and set a transmission format suchas a space multiplexing number to be used for space multiplexing, amodulation scheme, an M-ary modulation number and a coding rate for eachsubcarrier, and since the amount of processing increases as the numberof subcarriers increases, burdens are imposed on a radio communicationapparatus setting the transmission format and the scale of the apparatusis increased.

It is an object of the present invention to provide a radiocommunication apparatus and radio communication method capable ofreducing a burden when setting a transmission format and suppressingincreases in the scale of the apparatus.

Means for Solving the Problem

The radio communication apparatus according to the present invention isa radio communication apparatus that carries out radio transmission byapplying a multicarrier scheme to space multiplexing transmission,including a detection section that detects adaptability to spacemultiplexing transmission for each divided band obtained by dividing acommunication band of multicarrier transmission and to which a pluralityof subcarrier signals belong; and a setting section that sets atransmission format to be used to carry out radio transmission based onthe adaptability detected for each divided band.

The radio communication method according to the present invention is aradio communication method for a radio communication apparatus thatcarries out radio transmission by applying a multicarrier scheme tospace multiplexing transmission, including a detection step of detectingadaptability to space multiplexing transmission for each divided bandobtained by dividing a communication band of multicarrier transmissionand to which a plurality of subcarrier signals belong; and a settingstep of setting a transmission format used to carry out radiotransmission based on the adaptability detected for each divided band.

Advantageous Effect of the Invention

According to the present invention, it is possible to reduce a burdenwhen setting a transmission format and suppress increases in the scaleof the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 2 illustrates a relationship between a divided band and subcarriersignal according to Embodiment 1 of the present invention;

FIG. 3 is a block diagram showing main components of the configurationof a space multiplexing adaptability detection section according toEmbodiment 1 of the present invention;

FIG. 4 illustrates an example of operation when the base stationapparatus according to Embodiment 1 of the present invention carries outa radio communication with a mobile station apparatus;

FIG. 5 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention;

FIG. 6 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3 of the present invention;

FIG. 7 illustrates an example of operation when the base stationapparatus according to Embodiment 3 of the present invention carries outa radio communication with a mobile station apparatus;

FIG. 8A illustrates the frame configuration of an antenna-individuatedpilot signal transmitted by means of time division multiplexing from thebase station apparatus according to Embodiment 3 of the presentinvention;

FIG. 8B illustrates the frame configuration of an antenna-individuatedpilot signal transmitted by means of code division multiplexing from thebase station apparatus according to Embodiment 3 of the presentinvention;

FIG. 8C illustrates the frame configuration of an antenna-individuatedpilot signal transmitted by means of a combination of time divisionmultiplexing and code division multiplexing from the base stationapparatus according to Embodiment 3 of the present invention;

FIG. 9 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 4 of the present invention;

FIG. 10 is a block diagram showing main components of the configurationof a space multiplexing adaptability detection section according toEmbodiment 4 of the present invention;

FIG. 11 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 5 of the present invention; and

FIG. 12 illustrates a relationship between divided bands and subcarriersignals according to Embodiment 5 of the present invention.

DETAILED DESCRIPTION

Now, embodiments of the present invention will be explained in detailwith reference to the attached drawings. All the following embodimentswill explain cases where a transmission format is set in a transmissionsignal from a base station apparatus to a mobile station apparatus(hereinafter referred to as “downlink”).

(Embodiment 1)

FIG. 1 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention. Thisembodiment will explain a case with a radio communication system basedon a TDD (Time Division Duplex) scheme. Furthermore, this embodimentwill explain a case where space multiplexing adaptability is detectedbased on a reception result at the base station apparatus of atransmission signal from a mobile station apparatus to the base stationapparatus (hereinafter referred to as “uplink”) as an example.

Base station apparatus 100 shown in FIG. 1 includes Na antennas 102-1 to102-Na, Na duplexers 104-1 to 104-Na, Na reception system antennaelement sections 106-1 to 106-Na, space multiplexing adaptabilitydetection section 108, transmission format setting section 110,transmission format formation section 112, Na serial/parallel conversion(S/P) sections 114-1 to 114-Na and Na transmission system antennaelement sections 116-1 to 116-Na.

Furthermore, reception system antenna element sections 106-1 to 106-Nainclude separators 120-1 to 120-Na respectively. Transmission formatformation section 112 includes coding section 122, modulation section124 and space multiplexing section 126. Transmission system antennaelement sections 116-1 to 116-Na include mixers 128-1 to 128-Narespectively.

Furthermore, SM-capable mobile station apparatus 150 that carries out aradio communication with base station apparatus 100 includes Nr antennas152-1 to 152-Nr.

Antennas 102-1 to 102-Na are antennas in common with transmission andreception systems. Duplexers 104-1 to 104-Na output high-frequencysignals S-1 to S-Na received through antennas 102-1 to 102-Na toseparators 120-1 to 120-Na and wirelessly transmits high-frequencysignals S-1 to S-Na input from mixers 128-1 to 128-Na via antennas 102-1to 102-Na.

Separator 120-k (k=1 to Na) applies processing such as high-frequencyamplification and frequency conversion to high-frequency signal S-kinput from duplexer 104-k, then demultiplexes the signal into Nssubcarrier signals f₁-k to f_(Ns)-k and outputs the subcarrier signalsto space multiplexing adaptability detection section 108.

Space multiplexing adaptability detection section 108 detects spacemultiplexing adaptability, that is, adaptability to space multiplexingtransmission for each of Nd divided bands DB-1 to DB-Nd obtained bydividing a communication band to which Ns subcarrier signals f₁-k tof_(Ns)-k belong into Nd portions (Nd is a natural number: Ns>Nd≧1) andoutputs detection results #1 to #Nd to transmission format settingsection 110.

The number of subcarrier signals which belong to respective dividedbands DB-1 to DB-Nd need not always be equal, but it is assumed that, inthis embodiment explained below, Nc (Nc=Ns/Nd) subcarrier signalsuniformly belong to respective divided bands DB-1 to DB-Nd. Therelationship between the divided bands and subcarrier signals is asshown in FIG. 2 and Nc subcarrier signals exist in divided bands. On theother hand, when the number of subcarrier signals which belong to therespective divided bands are different, the number of subcarrier signalswhich belong to the mth divided band DB-k is expressed as Nc(m) andsatisfies the relationship in following (Equation 1).

$\begin{matrix}{{Ns} = {\sum\limits_{m = 1}^{Nd}{{Nc}(m)}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, the internal configuration of space multiplexing adaptabilitydetection section 108 will be explained using FIG. 3. Space multiplexingadaptability detection section 108 includes Nd divided band processingsections 156-1 to 156-Nd corresponding to divided band DB-m (m=1 to Nd).However, FIG. 3 only shows the configuration of divided band processingsection 156-1 that performs processing on divided band DB-1 forconvenience of explanation. The configurations of the remaining dividedband processing sections 156-2 to 156-Nd are similar to theconfiguration of divided band processing section 156-1, and thereforeexplanations thereof will be omitted. FIG. 3 takes a case where thenumber of subcarrier signals which belong to one divided band is 2 forexample and subcarrier signals f₁-k, f₂-k belong to divided band DB-1.

Divided band processing section 156-m includes replica generationsection 160 that generates replicas of pilot signals which are knownsignals embedded in their respective subcarrier signals f_(n(m))-1 tof_(n(m))-Na, correlation calculation sections 170-n-1 to 170-n-Na (n=1to Nc) that calculate correlation values between reception pilotsymbols, which are included in the respective subcarrier signalsf_(n(m))-1 to f_(n(m))-Na, and generated replicas, correlation matrixgeneration section 180 that generates a correlation matrix based on thecalculated correlation values, and adaptability evaluation functioncalculation section 190 that calculates an adaptability evaluationfunction for evaluating adaptability to space multiplexing transmissionbased on the correlation matrix generated. Here, n(m) denotes asubcarrier signal number which belongs to divided band DB-m.

Note that divided band processing section 156-m need not use allsubcarrier signals f_(n(m))-1 to f_(n(m))-Na which belong to dividedband DB-m. For example, it is possible to puncture some of subcarriersignal f_(n(m))-1 to f_(n(m))-Na and then carry out processing ondivided band DB-m. When the subcarrier signals are punctured, it isdifficult to improve the detection accuracy of adaptability to spacemultiplexing transmission but it is possible to obtain the effect ofreducing the amount of processing calculation.

Correlation calculation section 170-n-k carries out correlationcalculations to calculate correlation values between the generatedreplicas and the reception pilot symbols included in subcarrier signalsf_(n(m))-1 to f_(n(m))-Na. Assuming here that a pilot signal is r(s)(s=1 to Np, Np is the number of pilot signal symbols), correlationcalculation section 170-n-k calculates correlation value h_(nk) bycarrying out a correlation calculation shown in (Equation 2), where Nodenotes an oversampling number corresponding to a symbol and “*” denotesa complex conjugate transposition operator.

$\begin{matrix}{h_{nk} = {\frac{1}{Np}{\sum\limits_{s = 1}^{Np}{{f_{n - k}\left( {t_{0} + {{No} \cdot \left( {s - 1} \right)}} \right)}{r^{*}(s)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Correlation matrix generation section 180 generates correlation matrix Rshown in (Equation 4) using a column vector, that is, correlation vectorVn calculated for subcarriers according to (Equation 3) based oncalculated correlation value h_(nk), where n=1 to Nc, k=1 to Na, Tdenotes a vector transposition operator and H denotes a complexconjugate transposition operator.

$\begin{matrix}{V_{n} = \begin{bmatrix}h_{n,1} & {h_{n,2}\mspace{14mu}\ldots\mspace{14mu} h_{n,{Na}}}\end{bmatrix}^{T}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack \\{R = {\frac{1}{Nc}{\sum\limits_{n = 1}^{Nc}{V_{n}V_{n}^{H}}}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

That is, when correlation matrix R is generated, as shown in (Equation4) above, correlation matrix (VnVn^(H)) (hereinafter referred to as“auto-correlation”) is calculated from correlation vector Vn.Furthermore, correlation matrix R is obtained by integratingauto-correlations. In this embodiment, the auto-correlations areintegrated by summing up the auto-correlations associated with therespective subcarrier signals. By so doing, it is possible to emphasizecomponents corresponding to subcarrier signals in higher qualityreception states more and improve the accuracy of setting a transmissionformat.

Adaptability evaluation function calculation section 190 performseigenvalue expansion of generated correlation matrix R and determines Naeigenvalues λ_(k). Furthermore, calculated eigenvalues λ_(k) are sortedin descending order and subscripts are assigned from the maximumeigenvalue. Adaptability evaluation function values A and B shown in(Equation 5) and (Equation 6) are generated and detection results #mincluding them are output as space multiplexing adaptability of dividedband DB-m. Obtaining space multiplexing adaptability including aplurality of function values from calculated eigenvalue λ_(k) makes itpossible to provide a plurality of indices to decide whether or not theyare suitable for space multiplexing and improve the decision accuracycompared to a case where a decision is made using only one index. Here,adaptability evaluation function value A shows a signal to noise ratio(SNR) of a received signal from mobile station apparatus 150.Furthermore, adaptability evaluation function value B is one measure toevaluate a spatial spread. Note that since correlation matrix R is aHermitean matrix, its eigenvalues are real numbers.

$\begin{matrix}{{A\left( {\lambda_{1},\lambda_{2},\lambda_{Na}} \right)} = \frac{\lambda_{1}}{\lambda_{Na}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack \\{{B\left( {\lambda_{1},\lambda_{2},\lambda_{Na}} \right)} = \frac{\lambda_{2} - \lambda_{Na}}{\lambda_{1} - \lambda_{Na}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Transmission format setting section 110 sets a transmission format in acommunication band based on adaptability evaluation function values A, Bincluded in each detection result #m.

More specifically, transmission format setting section 110 comparesadaptability evaluation function values A, B of each divided band DB-mwith predetermined numbers respectively. As a result of this comparison,if both adaptability evaluation function values A and B are greater thanthe predetermined numbers, it is decided that the level of the receivedsignal is high and the spatial spread is large, that is, it is decidedto be suitable for space multiplexing transmission and a transmissionformat is set such that space multiplexing transmission is performed onthe downlink. On the other hand, when any one of adaptability evaluationfunction values A and B is equal to or falls below the predeterminedvalue, it is decided that the SNR is low or spatial spread is small andit is not suitable for space multiplexing transmission and atransmission format (space multiplexing number=1) is set such that spacemultiplexing transmission is not performed on the downlink andtransmission with directivity is performed on one channel.

A transmission format is set by determining the space multiplexingnumber of a communication band, modulation scheme, coding rate andweighting factor for transmission/reception (hereinafter referred to as“transmission/reception weight”). When the space multiplexing number ofthe communication band is calculated, transmission format settingsection 110 calculates a distribution of the space multiplexing numberscorresponding to divided bands DB-m and designates a space multiplexingnumber which accounts for the largest portion as the space multiplexingnumber of the communication band.

Furthermore, transmission format setting section 110 generates atransmission format control signal for reporting the set transmissionformat and outputs the signal to transmission format formation section112.

Transmission format setting section 110 may also carry out processing ofadaptively changing and setting an M-ary modulation number (modulationscheme) at modulation section 124 and a coding rate at coding section122 in accordance with adaptability evaluation function value A. Forexample, since adaptability evaluation function value A indicates an SNRof the received signal, transmission format setting section 110decreases the coding rate at coding section 122 and increases the M-arymodulation number at modulation section 124 as the channel qualityincreases. The set M-ary modulation number (modulation scheme) andcoding rate are reported as a transmission format control signal totransmission format formation section 112 together with the spacemultiplexing number.

Furthermore, the predetermined number used for the comparison withadaptability evaluation function value B may be changed in conjunctionwith adaptability evaluation function value A. In this case, forexample, it might be considered that the predetermined number used forthe comparison with adaptability evaluation function value B may bedecreased as adaptability evaluation function value A increases. By sodoing, it is possible to adaptively control the transmission formatsetting based on the spatial spread according to the reception quality(SNR in this embodiment).

Coding section 122 codes a transmission data sequence based on thecoding rate indicated in the transmission format control signal.

Modulation section 124 modulates the coded transmission data sequencebased on the M-ary modulation number (modulation scheme) indicated inthe transmission format control signal.

Space multiplexing section 126 divides the modulated transmission datasequence into the same number of portions as the space multiplexingnumber indicated in the transmission format control signal, multiplieseach divided transmission data sequence by a transmission weight andoutputs the multiplication results to S/P sections 114-1 to 114-Na.

S/P sections 114-1 to 114-Na convert in a serial-to-parallel manner thetransmission data sequence input from space multiplexing section 126,whereby the transmission data sequence becomes a multicarrier signalconverted to data sequences in a one-to-one correspondence withsubcarrier signals. Mixers 128-1 to 128-Na mix the multicarrier signalsinput from S/P sections 114-1 to 114-Na and output the mixed signals toduplexers 104-1 to 104-Na.

Next, the operation of base station apparatus 100 having the abovedescribed configuration when wirelessly communicating with mobilestation apparatus 150 will be explained. FIG. 4 illustrates an exampleof operation when base station apparatus 100 wirelessly communicateswith mobile station apparatus 150. Here, a procedure will be explainedin a space multiplexing transmission mode in a case of transiting from anormal transmission mode in which a transmission format for spacemultiplexing transmission is not used to a space multiplexingtransmission mode in which the transmission format for spacemultiplexing transmission is used.

First, after frame synchronization and symbol synchronization areestablished, mobile station apparatus 150 transmits antenna-individuatedpilot signals for space multiplexing transmission by means of timedivision or code division from antennas 152-1 to 152-Nr (S1100).

Correlation calculation section 170-n-k of base station apparatus 100carries out channel estimation, that is, estimates Nr×Na channelestimation values h(j, k) (S1200), using the receivedantenna-individuated pilot signals. Here, j=1 to Nr. Next, adaptabilityevaluation function calculation section 190 estimates reception qualityof antennas 102-1 to 102-Na for each mobile station apparatus (S1300).

Transmission format setting section 110 performs singular valuedecomposition to channel matrix H in which channel estimation value h(j,k) is expressed with a matrix as shown in (Equation 7). Right singularvalue vectors corresponding to Nm singular values λ_(j) in descendingorder are designated as transmission weights (transmission weightvectors) for base station apparatus 100, and left singular value vectorscorresponding to singular values are designated as reception weights(reception weight vectors) at mobile station apparatus 150. Nm is anatural number that satisfies 1≦Nm<min(Nr, Na). This makes it possibleto perform Nm space multiplexing transmissions. The above describedoperation is carried out for each of the subcarrier signals. Thereception weights obtained are reported to mobile station apparatus 150(S1400).

$\begin{matrix}{H = \begin{bmatrix}{h\left( {1,1} \right)} & {h\left( {1,2} \right)} & \ldots & {h\left( {1,N_{a}} \right)} \\{h\left( {2,1} \right)} & {h\left( {2,2} \right)} & \ldots & {h\left( {1,N_{a}} \right)} \\\vdots & \vdots & \vdots & \vdots \\{h\left( {N_{r},1} \right)} & {h\left( {N_{r},2} \right)} & \ldots & {h\left( {1,N_{a}} \right)}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Mobile station apparatus 150 carries out processing corresponding toreception of data channels (user channels) of individual users based onthe reception weights (S1500). Base station apparatus 100 then startstransmission of dedicated user channels based on the transmissionweights (S1600) and mobile station apparatus 150 starts reception of thededicated user channels (S1700). The above-described operation makes itpossible to perform space multiplexing transmission in accordance withthe detection results of space multiplexing adaptability.

Thus, this embodiment takes advantage of a high spatial spectrumcorrelation between adjacent subcarrier signals, divides a communicationband into a plurality of divided bands DB-1 to DB-Nd, combinescorrelation vectors Vn obtained from subcarrier signals which belong torespective divided bands DB-1 to DB-Nd to generate correlation matrix R,detects space multiplexing adaptability for each of the divided bandsusing generated correlation matrix R, and therefore, it is possible todetect a spatial spread of an average arriving path of subcarriersignals which belong to each of the respective divided bands. Therefore,by appropriately setting bandwidths of the divided bands and detectingspace multiplexing adaptability for each of the divided bands, it ispossible to reduce the amount of processing calculation compared to thedetection of space multiplexing adaptability conducted for each of thesubcarrier signals and suppress increases in the scale of the apparatus.This embodiment sets the transmission format of communication bands atone time, and therefore, it is possible to drastically reduce the amountof processing calculation compared to setting a transmission format foreach of the subcarrier signals.

That is, this embodiment obtains an average spatial spreadcharacteristic of an arriving path of a group of subcarrier signalswhich belong to each of the divided bands, and therefore, it is possibleto introduce an evaluation index for evaluating the spatialcharacteristic of the group of subcarrier signals into spacemultiplexing transmission control. Since this evaluation index does notexist in the conventional technique, the conventional technique has noother choice but to set a transmission format for each of the subcarriersignals. Therefore, in a conventional art, a transmission format couldbe erroneously set when more errors occur in calculations of correlationvalues of subcarrier signals whose levels are dropped as a result ofoccurrence of a notch (level drop) in a specific band in thecommunication band depending on the propagation environment. On thecontrary, according to this embodiment, it is possible to set atransmission format in a unit of the group of subcarrier signals byintroducing the evaluation index and thereby prevent erroneous settingsin the aforementioned case.

Furthermore, this embodiment allows switching to a space multiplexingtransmission mode only when the state of a propagation path is decidedto be suitable for space multiplexing transmission, and can therebyprevent drops in the effective transmission rate due to insertion ofunnecessary pilot signals in a propagation path unsuitable for spacemultiplexing transmission, and prevent increases in power consumptiondue to unnecessary calculation processing.

The configuration of base station apparatus 100 is not limited to theabove described one. For example, a configuration with which dividedbands are changed adaptively in accordance with a propagationenvironment may be added to the above described configuration. Forexample, a configuration with which divided bands are changed based on acorrelation bandwidth (coherent bandwidth) may be adopted. Thisconfiguration can provide an optimum tradeoff between the accuracy oftransmission format setting and the amount of calculation.

Furthermore, the configuration of space multiplexing adaptabilitydetection section 108 is not limited to the above described one. Forexample, a configuration calculating evaluation values on the mobilityof mobile station apparatus 150 including an estimated moving speed andDoppler frequency estimate of mobile station apparatus 150 may be addedto the above described configuration. In this case, since a delay isproduced due to SM assignment processing, when mobile station apparatus150 is in a state of a predetermined or higher mobility, a transmissionformat that prevents SM transmission is set to mobile station apparatus150. This stabilizes space multiplexing transmission.

Furthermore, this embodiment explained the case where the radiocommunication apparatus of the present invention is applied to basestation apparatus 100 and explained the setting of a transmission formaton a downlink, but it is also possible to apply the radio communicationapparatus of the present invention to mobile station apparatus 150 tothereby enable setting of a transmission format on an uplink.

Furthermore, adaptability evaluation function values A, B are notlimited to the above described ones. In addition, as adaptabilityevaluation function value A, it is also possible to use power of areceived signal (RSSI: Received Signal Strength Indicator), use anaverage signal level of a received pilot signal or use an SNR in which Sis the average signal level of a received pilot signal and N is adistribution situation of instantaneous pilot received signals.Furthermore, adaptability evaluation function value B may also becalculated based on the spread of an angle spectrum used to estimate adirection of arrival of paths. In this case, by conveniently performingvariable sweeping of θ that means the direction of arrival of paths inangle spectrum evaluation function F(θ) as shown in (Equation 8) andcalculating a spectral spread in a direction of a peak of the anglespectrum, it is possible to obtain adaptability evaluation functionvalue B. Here, a(θ) indicates direction vectors of antennas 102-1 to102-Na and can be expressed as shown in (Equation 9) when antennas 102-1to 102-Na form an equidistant rectilinear array. Furthermore, d denotesan antenna interval and λ denotes a wavelength in a carrier frequencyband.

$\begin{matrix}{{F(\theta)} = {{a(\theta)}^{H}{{Ra}(\theta)}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack \\{{a(\theta)} = \begin{bmatrix}1 \\{\exp\left\{ {{- j}\; 2\pi\;{d \cdot 1 \cdot \sin}\;{\theta/\lambda}} \right\}} \\\vdots \\{\exp\left\{ {{- j}\; 2\pi\;{d \cdot \left( {{Na} - 1} \right) \cdot \sin}\;{\theta/\lambda}} \right\}}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

Here, a Fourier method is used, but it is also possible to use an anglespectrum according to an eigenvalue decomposition technique such as awell-known MUSIC method and ESPRIT method or a high resolution techniquefor estimation of direction of arrival of path, such as Capon methodincluding inverse matrix calculation of a correlation matrix.

Furthermore, a space smoothing technique may be applied to correlationmatrix R to suppress a correlated wave. However, when the number ofsubcarrier signals which belong to each of the divided bands is smallerthan the number of antennas, the number of ranks of correlation matrix Rwhich is the output of correlation matrix generation section 180 may notbecome full. For this reason, it is necessary to conveniently select adirection estimation algorithm according to the number of subcarriersignals which belong to each of the divided bands or according to thesum of the number of subcarrier signals and the number of paths.Furthermore, when the configuration of antennas 102-1 to 102-Na is anequidistant rectilinear array arrangement, it is also possible to applyspace smoothing processing to correlation matrix R obtained atcorrelation matrix generation section 180 or apply processing ofestimating the direction of arrival using a beam space which ismultiplied by a unitary conversion matrix and whose directional vectorsare thus transformed to real numbers.

Correlation matrix generation section 180 may generate correlationvector z shown in (Equation 10) below instead of correlation matrix Rshown in (Equation 4) above. In this case, adaptability evaluationfunction calculation function 190 calculates adaptability evaluationfunction value A(z) shown in (Equation 11) below instead of adaptabilityevaluation function value A shown in (Equation 5) above and calculatesadaptability evaluation function value B(z) shown in (Equation 12) belowinstead of adaptability evaluation function value B shown in (Equation6) above.

$\begin{matrix}{\mspace{79mu}{z = {\frac{1}{Nc}{\sum\limits_{n = 1}^{Nc}{V_{n,1}^{*}V_{n}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack \\{{A(z)} = \frac{z_{1}}{\frac{1}{NcNp}{\sum\limits_{n = 1}^{Nc}{\sum\limits_{s = 1}^{Np}{{{{f_{n - 1}\left( {t_{0} + {{No}\left( {s - 1} \right)}} \right)}{r^{*}(s)}} - h_{n,1}}}^{2}}}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack \\{\mspace{79mu}{{B(z)} = \frac{z_{1}}{z_{2}}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

That is, SNR evaluation (=S/N) is performed using pilot signal r(s)transmitted from mobile station apparatus 150 first. In this evaluation,adaptability evaluation function value A(z) shown in (Equation 11) isused. Here, z_(k) denotes a kth element in correlation vector z shown in(Equation 10). The correlation between the signals received at antennas102-1 to 102-Na using correlation vector z is evaluated by calculatingadaptability evaluation function value B(z) shown in (Equation 12).

Furthermore, this embodiment explained the configuration in whichcorrelation matrix R is generated using known pilot signals with acombination of replica generation section 160, correlation calculationsection 170-n-k and correlation matrix generation section 180 in FIG. 3,but the internal configuration of space multiplexing adaptabilitydetection section 108 is not limited to this. For example, it is alsopossible to apply a technique of calculating a correlation matrixwithout using any pilot signals. In this case, it is possible tocalculate a correlation matrix by calculating a correlation valuebetween different branches in the array antenna. The element (j, k) ofcorrelation matrix Rb calculated here can be expressed by (Equation 13)below. Nb is the predetermined number of pieces of sample data. Thistechnique requires no pilot signals, and can thereby suppress a decreasein the transmission efficiency caused by insertion of pilot signals.Furthermore, similar processing is also applicable to correlation vectorz.

$\begin{matrix}{r_{jk} = {\frac{1}{Nb}{\sum\limits_{s = 1}^{Nb}{{f_{n - j}^{*}(t)}{f_{n - k}(t)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

Furthermore, in this embodiment, the subcarrier signals transmitted asthe multicarrier signals may also be subcarrier signals which have beensubjected to orthogonal frequency division multiplexing. In this case,frequencies at which subcarrier signals are orthogonal to one anotherwithin an OFDM symbol period are selected and used. Furthermore, thisembodiment is also applicable to an MC-CDMA (MultiCarrier—Code DivisionMultiple Access) scheme in which transmission signals are code divisionmultiplexed in the frequency axis direction. In this case, it ispossible to realize operations and effects similar to those describedabove by calculating the correlation value of each subcarrier signal foreach user using a pilot signal embedded in the subcarrier signal andmultiplexed for each individual user.

(Embodiment 2)

FIG. 5 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention. The basestation apparatus according to this embodiment has the basicconfiguration similar to that of the base station apparatus explained inEmbodiment 1 and the same components are assigned the same referencenumerals and detailed explanations thereof will be omitted.

The base station apparatus 200 shown in FIG. 5 includes Nd transmissionformat formation sections 112-1 to 112-Nd having the same internalconfigurations as that of transmission format formation section 112explained in Embodiment 1, Nd sets of S/P sections 114-1-1 to 114-1-Na,. . . , 114-Nd-Na having the same internal configurations as those ofS/P sections 114-1 to 114-Na explained in Embodiment 1, transmissionformat setting section 202 instead of transmission format settingsection 110 explained in Embodiment 1 and S/P section 204 thatserial/parallel-converts a transmission data sequence to Nd datasequences.

A feature of the base station apparatus 200 of this embodiment is to seta transmission format of each divided band as opposed to base stationapparatus 100 of Embodiment 1 that sets a transmission format of thecommunication band.

Transmission format setting section 202 sets a transmission format fordivided bands based on adaptability evaluation function values A and Bincluded in detection results #m.

More specifically, transmission format setting section 202 comparesadaptability evaluation function values A and B of divided bands DB-mwith their respective predetermined numbers. As a result of thiscomparison, when both adaptability evaluation function values A, B aregreater than the predetermined numbers, it is decided that the level ofa received signal is high and the spatial spread is large. In otherwords, it is decided to be suitable for space multiplexing transmissionand a transmission format is set such that space multiplexingtransmission is performed on a downlink. On the other hand, when any oneof adaptability evaluation function values A, B is equal to or fallsbelow the predetermined value, it is decided that the SNR is low or thespatial spread is small and it is decided not to be suitable for spacemultiplexing transmission and a transmission format (space multiplexingnumber=1) is set such that transmission with directivity is performed onone channel without carrying out space multiplexing transmission on thedownlink.

The transmission format is set by calculating a space multiplexingnumber, modulation scheme, coding rate and transmission/reception weightfor each of the divided bands.

Furthermore, transmission format setting section 202 generates atransmission format control signal for reporting the transmission formatset for each divided band and outputs the transmission format controlsignal to transmission format formation sections 112-1 to 112-Nd.

Note that transmission format setting section 202 may also carry outprocessing of adaptively changing and setting the M-ary modulationnumber (modulation scheme) in modulation sections 124-1 to 124-Nd andcoding rates in coding sections 122-1 to 122-Nd in accordance withadaptability evaluation function value A. For example, sinceadaptability evaluation function value A indicates an SNR of a receivedsignal, transmission format setting section 202 decreases the codingrates at coding sections 122-1 to 122-Nd or increases the M-arymodulation number at modulation sections 124-1 to 124-Nd, as the channelquality improves. The set M-ary modulation number (modulation scheme)and coding rate are reported to transmission format formation sections112-1 to 112-Nd as the transmission format control signal together withthe space multiplexing number.

Furthermore, the predetermined number used for a comparison withadaptability evaluation function value B may also be changed inconjunction with adaptability evaluation function value A. In this case,this embodiment may be adapted in such a way that the predeterminednumber to be used for the comparison with adaptability evaluationfunction value B is decreased as adaptability evaluation function valueA increases.

As opposed to transmission format formation section 112 explained inEmbodiment 1 that forms the transmission format of the communicationband, transmission format formation sections 112-1 to 112-Nd form atransmission format for each divided band and output a transmission datasequence space-multiplexed (or not space-multiplexed) for each dividedband to mixers 128-1 to 128-Na via the corresponding S/P sections.

Thus, this embodiment takes advantage of the fact that the correlationin the spatial spectrum between adjacent subcarrier signals is high,divides the communication band into a plurality of divided bands DB-1 toDB-Nd, combines correlation vectors Vn obtained from each subcarriersignal which belongs to each of the divided bands DB-1 to DB-Nd togenerate correlation matrix R, detects space multiplexing adaptabilityfor each of the divided bands using generated correlation matrix R, andtherefore, it is possible to detect a spatial spread of average arrivingpaths of subcarrier signals which belong to each divided band.Therefore, by appropriately setting the bandwidths of the divided bandsand detecting space multiplexing adaptability for each of the dividedbands, it is possible to reduce the amount of processing calculationcompared to the detection of space multiplexing adaptability carried outfor each of the subcarrier signals and suppress increases in the scaleof the apparatus. Since a transmission format is set for each of thedivided bands in this embodiment, it is possible not only to reduce theamount of processing calculation but also to set an optimum transmissionformat for each divided band.

This embodiment explained the case where the radio communicationapparatus of the present invention is applied to base station apparatus200 and explained the setting of the transmission format on thedownlink, but it is also possible to apply the radio communicationapparatus of the present invention to the mobile station apparatus sideand thereby set a transmission format on the uplink.

Furthermore, this embodiment can also apply a technique of calculating acorrelation matrix without using pilot signals as explained using(Equation 13) in Embodiment 1.

(Embodiment 3)

FIG. 6 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3 of the present invention. The basestation apparatus according to this embodiment has the basicconfiguration similar to that of base station apparatus 100 explained inEmbodiment 1 and the same components are assigned the same referencenumerals and explanations thereof will be omitted. Furthermore, thisembodiment will explain a case with a radio communication system underan FDD (Frequency Division Duplex) scheme.

The base station apparatus 300 shown in FIG. 6 includes spacemultiplexing adaptability detection section 302 instead of spacemultiplexing adaptability detection section 108 explained in Embodiment1.

Furthermore, SM-based mobile station apparatus 350 that communicateswith base station apparatus 300 by radio includes Nr antennas 352-1 to352-Nr.

A feature of base station apparatus 300 of this embodiment is to detectspace multiplexing adaptability based on feedback information from amobile station apparatus as opposed to Embodiment 1 in which spacemultiplexing adaptability is detected based on a result of reception ofan uplink signal at the base station apparatus.

Space multiplexing adaptability detection section 302 extracts feedbackinformation from a signal received from the mobile station apparatus350. The feedback information is information including a channelestimation value calculated by mobile station apparatus 350 usingantenna-individuated pilot signals and measured reception quality.

Furthermore, space multiplexing adaptability detection section 302generates detection results #1 to #Nd for the respective divided bandsusing the extracted feedback information and outputs the detectionresults to transmission format setting section 110.

It is also possible to provide space multiplexing adaptability detectionsection 302 in mobile station apparatus 350 so that detection results #1to #Nd for the respective divided bands are generated in the mobilestation apparatus side and the results may be used as feedbackinformation to the base station apparatus side. Or it is also possibleto provide space multiplexing adaptability detection section 302 andtransmission format setting section 110 in mobile station apparatus 350so that detection results #1 to #Nd for the respective divided bands aregenerated in the mobile station apparatus and the setting results bytransmission format setting section 110 may be used as feedbackinformation to the base station apparatus side. Thus, by modifying theapparatus configuration on the mobile station apparatus side, it ispossible to reduce the amount of feedback information and increase theefficiency of frequency utilization.

Next, the operation of base station apparatus 300 in the above describedconfiguration that wirelessly communicates with mobile station apparatus350 will be explained. FIG. 7 illustrates an example of the operationwhen base station apparatus 300 wirelessly communicates with mobilestation apparatus 350. Here, a procedure will be explained in a spacemultiplexing transmission mode in a case of transiting from a normaltransmission mode in which a transmission format for space multiplexingtransmission is not used to a space multiplexing transmission mode inwhich a transmission format for space multiplexing transmission is used.

First, after frame synchronization and symbol synchronization areestablished, base station apparatus 300 transmits antenna-individuatedpilot signals for space multiplexing transmission from the respectiveantennas 102-1 to 102-Na (S3100). An antenna-individuated pilot signalis made up of a predetermined number of symbols Np.

Here, antenna-individuated pilot signals transmitted will be explainedwith reference to the accompanying drawings. FIG. 8A, FIG. 8B and FIG.8C show frame configurations of antenna-individuated pilot signals. Forexample, as shown in FIG. 8A, an antenna-individuated pilot signalAP_(k) having the same pattern or patterns orthogonal to each other(e.g., PN signal) may be transmitted by means of time divisionmultiplexing whereby a transmission timing is shifted from one antennato another. Furthermore, as shown in FIG. 8B, antenna-individuated pilotsignal AP_(k) may be transmitted by means of code division multiplexing.In this case, antenna-individuated pilot signal AP_(k) has patternsorthogonal to one another among the antennas.

Furthermore, as shown in FIG. 8C, antenna-individuated pilot signalAP_(k) may also be transmitted by means of a combination of timedivision multiplexing and code division multiplexing. That is, in thiscase, patterns orthogonal to one another are used forantenna-individuated pilot signals (e.g., AP₁ and AP₂ in FIG. 8C) whichshare a time division slot of the same time instant are used. Bytransmitting antenna-individuated pilot signals by means of thecombination of time division multiplexing and code divisionmultiplexing, it is possible to reduce overhead of time divisiontransmission in a case of the number of antennas Na of base stationapparatus 300 being large, which alleviates a reduction of orthogonalityin a propagation path during code division multiplexing.

When the number of antennas Na is sufficiently large or the spacemultiplexing number in SM is limited to a value smaller than the numberof antennas Na, it is not necessary to use all Na transmission systems.For example, it is also possible to transmit antenna-individuated pilotsignals from several ones of antennas 102-1 to 102-Na.

Mobile station apparatus 350 separates and receives antenna-individuatedpilot symbol AP_(k)(t) included in antenna-individuated pilot signalAP_(k) through antennas 350-1 to 350-Nr (t=1 to Np). Mobile stationapparatus 350 then performs channel estimation using separately receivedantenna-individuated pilot symbol AP_(k)(t) (S3200).

More specifically, mobile station apparatus 350 carries out acorrelation calculation between reception result r_(j, k)(t) ofantenna-individuated pilot symbol AP_(k)(t) at antenna 350-j (j=1 to Nr)of mobile station apparatus 350 and replica AP_(k)(t) of theantenna-individuated pilot signal generated inside of mobile stationapparatus 350 and thereby calculates channel estimation value h(j, k) asshown in (Equation 14). That is, Na×Nr channel estimation values h(j, k)arc calculated. “*” denotes a complex conjugate transposition operator.

$\begin{matrix}{{h\left( {j,k} \right)} = {\sum\limits_{t = 1}^{Np}{{{AP}_{k}^{*}(t)}{r_{j,k}(t)}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

At this time, it is also possible to save reception result r_(j, k)(t) aplurality of times and apply averaging processing to the plurality ofsaved reception results r_(j, k)(t). In this case, when the moving speedof mobile station apparatus 350 is sufficiently small, it is possible toreduce the influence of noise and improve the accuracy of channelestimation.

Mobile station apparatus 350 then estimates reception quality P(j, k) ofantenna-individuated pilot signals and antennas of mobile stationapparatus 350 (S3300). Here, received signal power, SIR (signal to noiseratio) and SNR or the like may be used as reception quality, but a casewill be explained where SNR is used as an example. When signal power isassumed to be S(j, k)=|h(j, k)|²/Np and noise power is calculated using(Equation 15) below, it is possible to estimate reception quality P(j,k) by calculating S(j, k)/N(j, k).

$\begin{matrix}{{N\left( {j,k} \right)} = {\frac{1}{Np}{\sum\limits_{t = 1}^{Np}{{{r_{j,k}(t)} - {S\left( {j,k} \right)}}}^{2}}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

Mobile station apparatus 350 then transmits calculated channelestimation value h(j, k) and reception quality P(j, k) to base stationapparatus 300 (S3400). With regard to the reception quality, instead oftransmitting Na×Nr reception quality P(j, k) values, it is also possibleto transmit averaged Na×Nr reception quality P(j, k) values as shown in(Equation 16) below to reduce feedback information. Furthermore, insteadof transmitting the averaged value, it is also possible to transmit amedian value or maximum value of Na×Nr reception quality P(j, k) values.

$\begin{matrix}{P_{s} = {\frac{1}{N_{a}N_{r}}{\sum\limits_{k = 1}^{Na}{\sum\limits_{j = 1}^{Nr}{P\left( {j,k} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

Space multiplexing adaptability detection section 302 of base stationapparatus 300 then extracts feedback information including channelestimation value h(j, k) and reception quality P(j, k) from the receivedsignal from mobile station apparatus 350. Then, transmission formatsetting section 110 decomposes channel matrix H which expresses channelestimation value h(j, k) in matrix as shown in (Equation 7) intosingular values. The right singular value vectors corresponding to Nmsingular values λ_(j) in descending order are designated as transmissionweights (transmission weight vectors) at base station apparatus 300 andthe left singular value vectors corresponding to singular values λ_(j)is designated as reception weight (reception weight vector) at mobilestation apparatus 350. This allows Nm space multiplexing transmission tobe performed. Here, it is also possible to carry out adaptivetransmission power control by applying a water pouring theorem tocalculated singular values λ_(j). The above described operation iscarried out for each of the subcarriers. The reception weight obtainedis reported to mobile station apparatus 350 (S3500). Steps S1500 toS1700 explained in Embodiment 1 are then executed.

In the above described operation, after base station apparatus 300transits to the space multiplexing mode, it is also possible to detectspace multiplexing adaptability based on the magnitudes of singularvalues obtained through singular value decomposition of channel matrixH.

Furthermore, when no transmission beam is formed using eigenvectors,that is, when BLAST type space multiplexing in which data sequencesdiffering from one antenna to another are transmitted is used, thechannel estimation result and reception quality calculation result neednot be fed back. In this case, mobile station apparatus 350 carries outreception processing on dedicated user channels to be multiplexed basedon the channel estimation result and reception quality calculationresult.

Thus, according to this embodiment, base station apparatus 300 detectsspace multiplexing adaptability for each of the divided bands based onfeedback information from mobile station apparatus 350, and therefore aradio communication system based on an FDD scheme can also realizeoperations and effects similar to those of Embodiment 1.

Note that the detection of space multiplexing adaptability for each ofthe divided bands at base station apparatus 300 based on feedbackinformation from mobile station apparatus 350 is also applicable to aradio communication system based on a TDD scheme.

Furthermore, this embodiment explained a case where the radiocommunication apparatus of the present invention is applied to basestation apparatus 300 and explained the setting of a transmission formaton the downlink, but it is also possible to set a transmission format onthe uplink by applying the radio communication apparatus of the presentinvention to mobile station apparatus 350.

Furthermore, as explained in Embodiment 1 using (Equation 13), thisembodiment can also use a technique of calculating a correlation matrixwithout using pilot signals.

(Embodiment 4)

FIG. 9 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 4 of the present invention. The basestation apparatus according to this embodiment has the basicconfiguration similar to that of base station apparatus 100 explained inEmbodiment 1 and the same components are assigned the same referencenumerals and explanations thereof will be omitted. Furthermore, thisembodiment will explain a radio communication system using an MC-CDMAscheme with which each subcarrier signal is directly spread in atime-axis direction.

Base station apparatus 400 shown in FIG. 9 includes space multiplexingadaptability detection section 402 instead of space multiplexingadaptability detection section 108 explained in Embodiment 1.

A feature of the base station apparatus of this embodiment is to detectpath timings using pilot signals embedded in their respective subcarriersignals from a mobile station apparatus and calculate a correlationvalue to be used for space multiplexing adaptability for each of thepath timings detected.

Space multiplexing adaptability detection section 402 detects spacemultiplexing adaptability for each of Nd divided bands DB-1 to DB-Ndobtained by dividing the communication band to which Ns subcarriersignals f₁-k to f_(Ns)-k belong into Nd portions and outputs detectionresults #1 to #Nd to transmission format setting section 110.

Here, the internal configuration of space multiplexing adaptabilitydetection section 402 will be explained using FIG. 10. Spacemultiplexing adaptability detection section 402 includes Nd divided bandprocessing sections 403-1 to 403-Nd corresponding to divided bands DB-m.FIG. 10 only shows the configuration of divided band processing section403-1 which processes divided band DB-1 for convenience of explanation.The configurations of the remaining divided band processing sections403-2 to 403-Nd are similar to the configuration of divided bandprocessing section 403-1 and explanations thereof will be omitted. FIG.10 shows a case where the number of subcarrier signals which belong toone divided band is 2 as an example and subcarrier signals f₁-k, f₂-kbelong to divided band DB-1.

Divided band processing section 403-m includes path search section 404-nthat detects timings of Ln arriving paths for each of the subcarriersignals using a pilot signal which is a known signal embedded insubcarrier signals f_(n(m))-k, replica generation sections 406-n-1 to406-n-Ln that generate replicas of the pilot signals, correlationcalculation sections 408-n-k-1 to 408-n-k-Ln that calculate correlationvalues between reception pilot symbols which are included in subcarriersignals f_(n(m))-k, and the generated replica, correlation matrixgeneration section 410 that generates a correlation matrix based on thecalculated correlation value, and adaptability evaluation functioncalculation section 412 that calculates an adaptability evaluationfunction for evaluating adaptability to space multiplexing transmissionbased on the generated correlation matrix.

Note that divided band processing section 403-m need not use allsubcarrier signals f_(n(m))-k which belong to divided band DB-m as inthe case of divided band processing section 156-m. For example, it isalso possible to puncture some of subcarrier signals f_(n(m))-k and thencarry out processing on divided band DB-m. When a subcarrier signal ispunctured, it is difficult to improve the detection accuracy ofadaptability to space multiplexing transmission, but it is possible toobtain an effect of reducing the amount of processing calculation.

Path search section 404-n creates a delay profile using a pilot signalembedded in subcarrier signals f_(n(m))-k and detects path timings usingthe delay profile created. Correlation value h_(nk)(t_(j)) at jth pathtiming t_(j) corresponding to nth subcarrier signal f_(n)-k received atkth antenna 102-k is expressed in (Equation 17) below. Here, suppose apilot signal is expressed with r(s).

$\begin{matrix}{{h_{nk}\left( t_{j} \right)} = {\sum\limits_{s = 1}^{Np}{{f_{n - k}\left( {t_{j} + {{No} \cdot \left( {s - 1} \right)}} \right)}{r^{*}(s)}}}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

The delay profile is generated using (1) a method of combining absolutevalues or squares of correlation value h_(nk)(t_(j)) of the same timing,(2) a method of generating a plurality of delay profiles by multiplyingcorrelation values h_(nk)(t_(j)) of the same timing by weights forforming directional beams, summing up the multiplication results andacquiring an absolute value or square thereof, or (3) a method ofcombining them. Furthermore, it is possible to suppress a noisecomponent by averaging the delay profile over a plurality of frames.

Correlation matrix generation section 410 generates correlation matrix Rshown in (Equation 19) using correlation vector Vn shown in (Equation18) based on calculated correlation value h_(nk)(t_(j)).

$\begin{matrix}{{V_{n}\left( t_{j} \right)} = \begin{bmatrix}{h_{n,1}\left( t_{j} \right)} & {{h_{n,2}\left( t_{j} \right)}\mspace{14mu}\ldots\mspace{14mu} h_{n,{{Na}{(t_{j})}}}}\end{bmatrix}^{T}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack \\{R = {\frac{1}{NcLn}{\sum\limits_{n = 1}^{Nc}{\sum\limits_{j = 1}^{Ln}{{V_{n}\left( t_{j} \right)}{V_{n}\left( t_{j} \right)}^{H}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

Adaptability evaluation function calculation section 412 applies aneigenvalue expansion to generated correlation matrix R as in the case ofadaptability evaluation function calculation section 190 explained inEmbodiment 1 and obtains Na eigenvalues λ_(k). Furthermore, calculatedeigenvalues λ_(k) are sorted in descending order and assigned subscriptsare assigned from the maximum one. Adaptability evaluation functionvalues A and B shown in (Equation 5) and (Equation 6) are generated andthese are output as detection result #m.

Thus, this embodiment detects path timings using a pilot signal embeddedin each subcarrier signal from mobile station apparatus 150, calculatesa correlation value to be used to detect space multiplexing adaptabilityfor each of the detected path timings, and therefore, it is possible todetect adaptability for each of the divided bands including multipathsignals arriving at base station apparatus 400 and improve the detectionaccuracy by a path diversity effect.

Note that correlation matrix generation section 410 may also generatecorrelation vector z shown in (Equation 20) below instead of correlationmatrix R shown in (Equation 19) above. In this case, adaptabilityevaluation function calculation section 412 calculates adaptabilityevaluation function value A(z) shown in (Equation 21) below instead ofadaptability evaluation function value A shown in (Equation 18) aboveand calculates adaptability evaluation function value B(z) shown in(Equation 22) below instead of adaptability evaluation function value Bshown in (Equation 19) above.

$\begin{matrix}{\mspace{79mu}{z = {\frac{1}{NcLn}{\sum\limits_{n = 1}^{Nc}{\sum\limits_{j = 1}^{Ln}{{V_{n,1}^{*}\left( t_{j} \right)}{V_{n}\left( t_{j} \right)}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack \\{{A(z)} = \frac{z_{1}}{\begin{matrix}{\frac{1}{NcLnNp}{\sum\limits_{n = 1}^{Nc}{\sum\limits_{j = 1}^{Ln}{\sum\limits_{s = 1}^{Np}{{{{f_{n - 1}\left( {t_{0} + {{No}\left( {s - 1} \right)}} \right)}{r^{*}(s)}} -}}}}}} \\{h_{n,1}}^{2}\end{matrix}}} & \left\lbrack {{Equation}\mspace{14mu} 21} \right\rbrack \\{\mspace{79mu}{{B(z)} = \frac{z_{1}}{z_{2}}}} & \left\lbrack {{Equation}\mspace{14mu} 22} \right\rbrack\end{matrix}$

That is, an SNR (=S/N) is evaluated using pilot signal r(s) transmittedfrom mobile station apparatus 150 first. In this evaluation,adaptability evaluation function value A shown in (Equation 21) is used.Here, z_(k) denotes the kth element in correlation vector z shown in(Equation 20). Next, the correlation between the signals received atantennas 102-1 to 102-Na is evaluated using correlation vector z bycalculating adaptability evaluation function value B(z) shown in(Equation 22).

Furthermore, this embodiment explained a case where the radiocommunication apparatus of the present invention is applied to basestation apparatus 400 and explained the setting of a transmission formaton the downlink, but it is also possible to set a transmission format onthe uplink by applying the radio communication apparatus of the presentinvention to the mobile station apparatus side.

Furthermore, in this embodiment, it is also possible to apply atechnique of calculating a correlation matrix without using any pilotsignals as explained in Embodiment 1 using (Equation 13).

(Embodiment 5)

FIG. 11 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 5 of the present invention. The basestation apparatus according to this embodiment has the basicconfiguration similar to that of base station apparatus 100 explained inEmbodiment 1 and the same components are assigned the same referencenumerals and explanations thereof will be omitted. Furthermore, thisembodiment will explain a radio communication system using amulticarrier scheme under which code division multiplexing is carriedout for a plurality of users through spreading in the frequency axisdirection.

Base station apparatus 500 shown in FIG. 11 includes divided bandchanging section 502 in addition to the components of base stationapparatus 100 explained in Embodiment 1.

A feature of the base station apparatus of this embodiment is to changethe bandwidths of the divided bands according to a spreading factor fora user channel subjected to code division multiplexing.

Divided band changing section 502 changes the bandwidths of the dividedband according to a spreading factor of a user channel subjected to codedivision multiplexing. That is, when the qth user channel is spread inthe frequency axis direction with spreading code sequence Sq(s) ofspreading factor SF(q) (that is, when a transmission data sequence isspread using SF(q) subcarrier signals), a group of subcarrier signalsused in the spreading processing is considered as one divided band.Thus, since the bandwidth of a divided band is changed according tospreading factor SF(q), the number of the divided bands Nd(q) in thecommunication band is variable.

Here, the relationship between the divided bands and subcarrier signalsis as shown in FIG. 12. The Ns subcarrier signals on the frequency axisare divided into Nd(q) divided bands according to spreading factorsSF(q) of user channels. Nc=SF(q) subcarrier signals exist in eachdivided band. Though similar operations and effects can also be obtainedeven when the number of subcarrier signals in each divided band isassumed to be w×SF(q) (w: natural number), this embodiment will beexplained assuming w=1.

Furthermore, divided band changing section 502 assigns divided bandsDB-m whose bandwidths have been changed (m=1 to Nd(q) in thisembodiment) to Nd(q) divided band processing sections 156-m in spacemultiplexing adaptability detection section 108.

Thus, this embodiment changes the bandwidth (number of subcarriersignals) of a divided band according to the spreading factor of users toa plurality of user channels that are code division multiplexed in thefrequency axis direction and therefore it is possible to detect spacemultiplexing adaptability for each channel to be spread and transmitted.

The feature of base station apparatus 500 explained in this embodimentmay also be applied to base station apparatus 200 explained inEmbodiment 2. Since base station apparatus 200 sets a transmissionformat for each of the divided bands, applying the feature of thisembodiment makes it possible to set an optimum transmission format foreach of the channels to be spread and transmitted and carry out optimumspace multiplexing transmission for each channel. In this case, when themobile station apparatus receives space multiplexed data, it is possibleto perform reception processing in units of spreading symbols (or aninteger multiple thereof).

Furthermore, the feature of base station apparatus 500 explained in thisembodiment may also be applied to base station apparatus 300 explainedin Embodiment 3. In this case, operations and effects similar to thosedescribed above can be realized.

Furthermore, this embodiment explained the transmission scheme in whicha multicarrier signal is spread in the frequency axis direction as anexample but the present invention is also applicable to a transmissionscheme in which a multicarrier signal is spread in both the frequencyaxis and time axis directions. Under such a transmission scheme,spreading factor SF(q) of the qth user can be expressed as the productof spreading factor SF_(f)(q) in the frequency axis direction andspreading factor SF_(t)(q) in the time axis direction as shown in(Equation 23). For this reason, when this transmission scheme is appliedto base station apparatus 500, similar operations and effects can berealized by changing the bandwidths of the divided bands based onspreading factor SF₊(q) in the frequency axis direction.SF(q)=SF _(f)(q)×S F _(t)(q)  [Equation 23]

Furthermore, in this embodiment, it is also possible to use a techniqueof calculating a correlation matrix without using any pilot signal asexplained in Embodiment 1 using (Equation 13).

The present application is based on Japanese Patent Application No.2003-280557 filed on Jul. 28, 2003, and Japanese Patent Application No.2004-213588 filed on Jul. 21, 2004, the entire contents of which areexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The radio communication apparatus and radio communication methodaccording to the present invention have the effect of alleviating aburden in setting a transmission format and suppressing increases in thescale of the apparatus, and are suitable for use in a digital radiocommunication system using a multicarrier scheme.

The invention claimed is:
 1. An integrated circuit configured to controla process of communicating with a reception apparatus using a pluralityof divided frequency bands in a communication band, the communicationband being divided into the plurality of divided frequency bands andeach divided frequency band including a plurality of subcarriers, theintegrated circuit comprising: generator circuitry configured togenerate information per divided frequency band according to a formatincluding information on a spatial multiplexing number and informationon a spatial multiplexing weight for use in a spatial multiplexingtransmission with the reception apparatus; and a transmitter configuredto transmit the generated information to the reception apparatus.
 2. Theintegrated circuit according to claim 1, comprising: control circuitryconfigured to control the process; and at least one output, coupled tothe control circuitry, configured to output the generated informationfor transmission to the reception apparatus.
 3. The integrated circuitaccording to claim 2, wherein the format further includes one or more ofinformation on a modulation scheme and information on a coding rate. 4.The integrated circuit according to claim 2, further comprising:detector circuitry configured to detect a reception quality of a signaltransmitted from the reception apparatus per divided frequency band, andwherein the generator circuitry is configured to generate theinformation per divided frequency band according to the format based onthe detected reception quality per divided frequency band.
 5. Theintegrated circuit according to claim 2, wherein the format is set inaccordance with the spatial multiplexing number of the spatialmultiplexing transmission.
 6. An integrated circuit configured tocontrol a process of communicating with a transmission apparatus using aplurality of divided bands in a communication band, the communicationband being divided into the plurality of divided bands and each of theplurality of divided bands including a plurality of subcarriers, theintegrated circuit comprising: a transmitter configured to transmit asignal to the transmission apparatus, the signal being for use by thetransmission apparatus to set a format; and a receiver configured toreceive information per divided band, the information being generated bythe transmission apparatus according to the format including informationon a spatial multiplexing number and information on a spatialmultiplexing weight for use in a spatial multiplexing transmission withthe transmission apparatus, wherein one format corresponds to onedivided band of the plurality of divided bands.
 7. The integratedcircuit according to claim 6, comprising: control circuitry configuredto control the process; at least one output, coupled to the controlcircuitry, and configured to output the signal for transmission to thetransmission apparatus; and at least one input, coupled to the controlcircuitry, configured to receive the information transmitted from thetransmission apparatus.
 8. The integrated circuit according to claim 7,further comprising: detection circuitry configured to detect a receptionquality of a received signal transmitted from the transmissionapparatus, and wherein the transmitter is configured to transmit anindication of the reception quality of the received signal to thetransmission apparatus for use in setting the format.
 9. The integratedcircuit according to claim 7, wherein the format is set by thetransmission apparatus in accordance with the spatial multiplexingnumber of the spatial multiplexing transmission.
 10. An apparatus forcommunicating with a reception apparatus using a plurality of dividedfrequency bands in a communication band, the communication band beingdivided into the plurality of divided frequency bands and each dividedfrequency band including a plurality of subcarriers, the apparatuscomprising: an integrated circuit configured to generate information perdivided frequency band according to a format including information on aspatial multiplexing number and information on a spatial multiplexingweight for use in a spatial multiplexing transmission with the receptionapparatus; and a transmitter configured to transmit the generatedinformation to the reception apparatus.
 11. The apparatus according toclaim 10, further comprising: at least one output configured to outputcoupled to the circuitry, wherein the at least one output, in operation,outputs the generated information for transmission to the receptionapparatus.
 12. The apparatus according to claim 11, wherein the formatfurther includes one or more of information on a modulation scheme andinformation on a coding rate.
 13. The apparatus according to claim 11,wherein the integrated circuit is further configured to: detect areception quality of a signal transmitted from the reception apparatusper divided frequency band; and generate the information per dividedfrequency band according o the format based on the detected receptionquality per divided frequency band.
 14. The apparatus according to claim11, wherein the format is set in accordance with the spatialmultiplexing number of the spatial multiplexing transmission.
 15. Anapparatus for communicating with a transmission apparatus using aplurality of divided bands in a communication band, the communicationband being divided into the plurality of divided bands and each of theplurality of divided bands including a plurality of subcarriers, theapparatus comprising: a transmitter configured to transmit a signal tothe transmission apparatus, the signal being for use by the transmissionapparatus to set a format; a receiver configured to receive informationper divided band; an integrated circuit configured to process theinformation as generated by the transmission apparatus according to theformat including information on a spatial multiplexing number andinformation on a spatial multiplexing weight for use in a spatialmultiplexing transmission with the transmission apparatus, wherein oneformat corresponds to one divided band of the plurality of dividedbands.
 16. The apparatus according to claim 15, further comprising: atleast one output configured to output the signal for transmission to thetransmission apparatus; and at least one input configured to receive theinformation transmitted from the transmission apparatus.
 17. Theapparatus according to claim 16, wherein the integrated circuit isfurther configured to: detect a reception quality of a received signaltransmitted from the transmission apparatus; and transmit an indicationof the reception quality of the received signal to the transmissionapparatus for use in setting the format.
 18. The apparatus according toclaim 16, wherein the format is set by the transmission apparatus inaccordance with the spatial multiplexing number of the spatialmultiplexing transmission.